In this page, I'm examining the behavior of 'industrial-wind-turbine-generated' infrasound in initially impacting the occupied structures on affected properties (houses, rooms and barns), and subsequently in impacting the physical structures of people, livestock and wildlife.
I recommend the following website tool (courtesy of www.sengpielaudio.com) to help compare the relationship between the 'pitch', 'tone' or 'frequency' of atmospheric compressions (sound) and those compressions' actual physical 'lengths' ...
www.sengpielaudio.com/calculator-wavelength.htm
Standing waves are produced whenever two waves of identical frequency of compression interfere with one another while traveling opposite directions along the same medium. A standing wave pattern is a vibrational pattern created within a medium when the vibrational frequency of the source causes reflected frequencies of compression from one end of the medium to interfere with incident frequencies of compression from the source. This interference occurs in such a manner that specific points along the medium appear to have frequencies of compression that are standing still .. re-inforced into a stronger "standing wave".
The above definition may be a bit hard to visualize. The following example may prove easier to envision. This example is taken from How to Build a Small Budget Recording Studio from Scratch, By Mike Shea and Frederick Alton, Edition: 3 - 2002 - 352 pages. References to the book was made by Google Books preview at ... http://books.google.ca.
Chapter 1, page 2 describes how to find the fundamental frequency (or 1st harmonic) of a structure. In the example given, the sound studio in question has pair of parallel walls 20 feet apart (the room's length). One starts with the speed of sound in feet per second ... 1130 feet/second ... and divides it by twice the room's length (2L) ... to arrive at the fundamental frequency of resonance of the room which will set up a standing wave across that dimension.
Here's the calculation ...
1130 / 2L = structure's fundamental frequency
1130 / 40 = 28 Hz. (approx.)
It is worth noting that similar resonance will also occur between parallel walls which are 40, 80, 120 .etc feet apart.
In addition, frequencies of 56, 84, 112 Hz, .etc. would also generate "harmonic resonance" across this dimension of the structure.
Following is an illustrated example I've drawn up, of rooms producing four different "axial" standing waves within one structure.
Note: In situations where the incoming sound impacts a structure at other than 90 degrees, all four walls of the structure and their greater sum of dimensions can become involved, responding to even lower frequencies in the production of a "tangential standing wave".
The "axial" standing-wave effect can also be described as follows ... Houses, barns, and any partitioned structures have different depths and widths, as well as different orientations. When one of these structures is impacted at right-angles by low frequency sound and infrasound, the physically long compressions of which either equals twice that structure's depth (relative to that impact) or is an even divisor of the compressions' full length, a "standing wave" is generated. A resonating amplification results between the affected walls of the structure. While such a resonating amplification's full intensity is for the most part specific to being within the structure in question, it's secondary vibrations can extend somewhat beyond the actual 'receptor' structures for short distances. There have been accounts of burrowing animals abandonning the immediate vicinity of such structures.
This phenomenon cannot be measured by a simple sound meter's microphone being located outside at an equal distance from a wind turbine. The phenomenon is unique and dependant on a number of variables .. including the size, composition and orientation of the structure in question.
Second, pertaining to the impact of the unique range and sequence of frequencies of audible atmospheric compressions (sound waves) which produce an industrial wind turbine's "whoosh" ...
Skeletal structures (cranium, pelvis, etc.) have specific dimensions, dependant on orientation. When a range and sequence of sounds of specific frequencies impact these structures, momentary "standing waves" can be generated .. when half a sound frequency's actual wavelength either equals the structure's interior depth or its full length is an even divisor of the structure's depth. A resonating amplification results between the affected sides of the structure. As the a turbine "whoosh" sequences through its range of frequencies, organs located close by will either sense the amplified resonancies that occur at those critical frequencies.These amplified resonances will be actually sensed at much greater energy levels than an externally located sound meter's microphone would be able to pick-up.
These resonating amplifications are experientially subjective experiences. These phenomena cannot be measured by a simple sound meter's microphone. They are unique and dependant on a number of variables .. including the size, composition and orientation of the skeletal structures in question.
Subsequent to compiling this page to this point on July 1st 2009, I came across a document titled "Wind Turbine Acoustic Noise (2006) - A white paper prepared by the Renewable Energy Research Laboratory, Department of Mechanical and Industrial Engineering, University of Massachusetts at Amherst, MA". It can be downloaded in its entirety here .
On page 13, I found one graph to be of particular interest ...
It contains what I consider to be some serious omissions, as follow ...
- The "audible A-filtered level" is an averaged 45 dBA, in disregard of the full levels of the "impulsive peaks".
- The "inaudible level" of low frequency sound and infrasound is an averaged approximate 65 dBA, in disregard of the full levels of impulsive peaks ... and also in disregard of their "standing-wave resonance amplification" within structures.
- The "dB(Lin) level" (otherwise known as "full energy content of all frequencies") is an average of over 75 dB ... again disregarding the full levels of "impulsive peaks".
- Failure to indicate that since sound pressure amounts (energy in the sound) increases 2 times with approx. each 3 decibel increase, the low frequency sound and infrasound frequencies' averaged levels bear approximately 100 times the energy content of the "A-filtered" frequencies' averaged levels.
(Refer to the Sound Energy page.)
In my opinion, the way in which the air-pressure energy levels (decibels) are portrayed here, illustrates the limited and inadequate ways in which industry and government deal with the real issues at hand.
swaves.htm (August 1, 2009)